Pipefitter Valves, Fittings, and Supports 2 — Questions and Answers
Question 1: What is the primary difference between a 'full port' and a 'reduced port' ball valve?
- A full port valve has a bore equal to the pipe ID; a reduced port has a smaller bore that restricts flow (Correct answer)
- A full port valve handles higher pressure than a reduced port valve
- A full port valve can be used for throttling; a reduced port is for on/off service only
- A full port valve opens fully in a quarter turn; a reduced port requires multiple turns
Correct answer: A full port valve has a bore equal to the pipe ID; a reduced port has a smaller bore that restricts flow
A full port (full bore) ball valve has an internal bore equal to the pipe ID, providing no restriction. A reduced port has a smaller bore that increases velocity and pressure drop.
Full port (full bore) ball valves have a ball bore equal to the pipe nominal bore, resulting in minimal pressure drop and unrestricted flow — critical for pig-able pipelines, slurry services, and systems sensitive to pressure drop. Reduced port (standard port) valves have a ball bore one size smaller than the pipe, which reduces the valve cost but introduces a flow restriction. Ball valves are quarter-turn valves suitable for on/off service; they are not generally used for throttling because the partially-open position can cause valve seat erosion.
Question 2: What is a 'check valve,' and what is its function in a piping system?
- A self-actuating valve that allows flow in one direction only and prevents backflow (Correct answer)
- A manual valve used to check the position of other valves in the system
- A pressure relief valve that opens when pressure exceeds a set point
- A valve with a visual flow indicator to check that fluid is flowing
Correct answer: A self-actuating valve that allows flow in one direction only and prevents backflow
A check valve permits flow in one direction and automatically closes to prevent reverse flow (backflow) when flow stops or reverses.
Check valves are non-return valves that open when forward flow pressure exceeds a small cracking pressure, and close automatically when flow stops or reverses. Common types: swing check (disc swings on a hinge — for horizontal lines), lift check (disc lifts off seat — must be installed in horizontal lines), piston/wafer check (compact, spring-loaded), and dual plate (wafer-style, low pressure drop). Check valves are installed on pump discharge lines, compressor outlets, and any line where backflow would cause equipment damage or process contamination.
Question 3: What is the function of a 'pressure relief valve' (PRV) in a piping system?
- To automatically open and release excess pressure when system pressure exceeds the valve's set point, protecting the system from over-pressure (Correct answer)
- To reduce upstream pressure to a lower, constant downstream pressure
- To relieve vacuum conditions by admitting air into the piping system
- To control flow rate by throttling based on downstream pressure
Correct answer: To automatically open and release excess pressure when system pressure exceeds the valve's set point, protecting the system from over-pressure
A PRV (safety relief valve) opens automatically when pressure reaches its set point to release fluid and prevent over-pressure failure of the piping or vessel.
Pressure relief valves (PRVs or safety valves) are code-required safety devices (ASME Section VIII for vessels, ASME B31.3 for piping) that open automatically at a set pressure to discharge fluid and prevent system failure. Once pressure drops below the set point, the valve closes. PRVs are sized to relieve the maximum credible over-pressure scenario (blocked outlet, fire exposure, etc.). Safety valves (snap action) are used for gas/steam; safety relief valves work for both gas and liquid; relief valves (modulating) are used for liquid-only service.
Question 4: What is a 'spring hanger' used for in process piping systems?
- To support pipe weight while allowing controlled vertical movement due to thermal expansion or settling (Correct answer)
- To provide seismic restraint for pipe during earthquakes
- To maintain constant pipe slope in drain lines
- To anchor pipe to prevent any movement at a fixed point
Correct answer: To support pipe weight while allowing controlled vertical movement due to thermal expansion or settling
Spring hangers support the pipe weight while permitting controlled vertical movement from thermal expansion, preventing stress transfer to nozzles or equipment.
Spring hangers (variable spring hangers or constant effort hangers) are used where process piping undergoes significant vertical thermal movement. Variable spring hangers support pipe weight through a coiled spring that deflects as the pipe moves — the supporting force changes slightly with movement. Constant effort hangers use a spring-and-lever mechanism to provide constant support force throughout the travel range. They are commonly used at equipment nozzles (pumps, vessels, exchangers) to prevent thermal expansion forces from overloading the nozzle.
Question 5: What is the purpose of the 'body-to-bonnet' joint on a gate valve, and how is it typically sealed?
- It seals the pressure boundary where the bonnet (containing the stem and packing) joins the valve body, typically with a gasket and bolted connection (Correct answer)
- It connects the valve body to the pipeline flanges using a ring-type joint
- It seals the stem penetration to prevent external leakage along the stem
- It provides the connection point for the valve actuator or handwheel
Correct answer: It seals the pressure boundary where the bonnet (containing the stem and packing) joins the valve body, typically with a gasket and bolted connection
The body-to-bonnet joint is a pressure boundary joint sealed with a gasket (spiral wound or ring joint) and secured with studs/nuts to contain process fluid.
The body-to-bonnet joint is a critical pressure boundary on gate, globe, and check valves. It seals the joint between the valve body (lower half containing the seats and bore) and the bonnet (upper portion containing the stem, gland, and packing). It is sealed with a gasket (flat ring, spiral wound, or ring-type joint for high pressure) and secured with studs and nuts. This joint may require periodic retorquing under thermal cycling. In screwed bonnet valves (small sizes), threads and thread sealant provide the seal.
Question 6: What is a 'pipe shoe' and when is it used instead of a standard pipe clamp?
- A shoe is a cradle welded to the pipe bottom that sits on a structural support, used for insulated pipe to maintain insulation integrity (Correct answer)
- A shoe is a rubber-lined clamp used on copper pipe to prevent galvanic corrosion
- A shoe is a sliding foot on a spring hanger that allows lateral movement
- A shoe is a protective cover for pipe threads during construction
Correct answer: A shoe is a cradle welded to the pipe bottom that sits on a structural support, used for insulated pipe to maintain insulation integrity
A pipe shoe is a steel cradle welded to the pipe and resting on a structural support, used on insulated pipe to transfer load without compressing or damaging the insulation.
Pipe shoes are used on insulated pipes to avoid compressing or damaging insulation at support points. The shoe is a steel 'cradle' or 'sled' welded to the bare pipe. It extends below the insulation and sits directly on the pipe rack, structural beam, or support shoe. This keeps the load path in the steel while the insulation remains undamaged. Shoes are sized to extend beyond the insulation OD and may include wear plates for sliding supports. They are specified in the piping support standard for insulated process lines.
Pipefitter Valves, Fittings, and Supports 2
What is the primary difference between a 'full port' and a 'reduced port' ball valve?